DebugInfo: Avoid emitting null members for nodebug nested typedefs

Only comes up for CodeView, since it forcibly emits even unused nested
typedefs.

Part of issue #122350

Author: dwblaikie

clang/lib/CodeGen/CGDebugInfo.cpp

@@ -1907,8 +1907,8 @@ void CGDebugInfo::CollectRecordNestedType(
   if (isa<InjectedClassNameType>(Ty))
     return;
   SourceLocation Loc = TD->getLocation();
-  llvm::DIType *nestedType = getOrCreateType(Ty, getOrCreateFile(Loc));
-  elements.push_back(nestedType);
+  if (llvm::DIType *nestedType = getOrCreateType(Ty, getOrCreateFile(Loc)))
+    elements.push_back(nestedType);
 }
 
 void CGDebugInfo::CollectRecordFields(

clang/test/CodeGenCXX/debug-info-codeview-nodebug.cpp

@@ -0,0 +1,20 @@
+// RUN: %clang_cc1 -DSETNODEBUG=0 -gcodeview -emit-llvm -std=c++14 -debug-info-kind=limited %s -o - | FileCheck %s --check-prefix=YESINFO
+// RUN: %clang_cc1 -DSETNODEBUG=1 -gcodeview -emit-llvm -std=c++14 -debug-info-kind=limited %s -o - | FileCheck %s --check-prefix=NOINFO
+
+#if SETNODEBUG
+#define NODEBUG __attribute__((nodebug))
+#else
+#define NODEBUG
+#endif
+
+struct t1 {
+  using t2 NODEBUG = void;
+};
+void func6() {
+  t1 v1;
+}
+// YESINFO-DAG: !DIDerivedType(tag: DW_TAG_typedef, name: "t2"
+// NOINFO: [[ELEMENTS:!.*]] = !{}
+// NOINFO: !DICompositeType(tag: DW_TAG_structure_type, name: "t1", {{.*}}, elements: [[ELEMENTS]],
+// NOINFO-NOT:  !DIDerivedType(tag: DW_TAG_typedef, name: "t2"
+